dataset/database update

Question

i have a webservice that returns a dataset holding all categories.
i want to enter these rows in the database by calling the data
adapter's update method.
i'm doing the following but no update to my database is made. why is
that?

Code:

        this.dsetMustaqbal = currentIssueWS.GetCategories(); 
    this.sqlDataAdapter1.Update(this.dsetMustaqbal ,"Categories)